Strain sensors are widely utilized for measuring and monitoring strain, pressure, force, and/or vibration in certain structures in order to provide inspection and flaw detection associated with such structures. Strain sensors can detect the magnitude of stress and load in various industrial and commercial applications. Examples of such applications include structural health monitoring applications such as industrial equipment condition monitoring, pipe and tank monitoring in oil and chemical industries, turbine engines, and in medical applications, to name a few.
A piezoelectric strain sensor takes advantage of the piezoelectric effect to measure pressure, acceleration, strain, and/or force by converting signals indicative of such conditions into electrical signals. The majority of prior art strain sensors are not suitable for manufacturing on a flexible substrate. Such strain sensors, if based on piezoelectric materials, also require complex electronics for collecting the sensor signal and operate with a low sensitivity. Traditional piezoresistive strain sensors have either a very low sensitivity (e.g., metallic sensors) or large power consumption (e.g., semiconductor piezoresistive sensors). Furthermore, the cost for manufacturing such sensors on a substrate increases the complexity of the resulting system and may result in a reduction in reliability.
Based on the foregoing, it is believed that a need exists for an improved field-effect piezoelectric strain sensor apparatus for detecting strain, vibration, and/or pressure. A need also exists for an improved method for fabricating the strain sensor apparatus on a flexible substrate by a low cost fabrication technique, as described in greater detail herein.